The invention relates to severing or cutting apparatus in general, and more particularly to improvements in apparatus for severing paper and/or other relatively thin flexible sheet materials. Still more particularly, the invention relates to improvements in so-called cross cutters which can be utilized to subdivide running webs or strips of flexible material into panels, sheets or lengths of desired size and shape.
Apparatus of the type to which the present invention pertains are disclosed, for example, in U.S. Pat. No. 4,201,102 granted May 6, 1980 to Rudszinat and in U.S. Pat. No. 4,255,998 granted Mar. 17, 1991 to Rudszinat.
As a rule, a cross cutter employs two rotary drum-shaped knife holders which are disposed at opposite sides of the path for a running web of paper, metallic foil, plastic foil or other relatively thin flexible sheet material. The holders are driven in synchronism so that their knives meet at a selected portion of the path for the web and sever the web transversely of the direction of advancement of the web toward a station where the separated panels, sheets or lengths are accepted by a transporting, stacking or other processing unit. Problems arise when the freshly formed leader of a relatively thin and readily flexible web exhibits a tendency to adhere to the one or the other knife holder immediately behind the locus of the cut, i.e., immediately behind the freshly formed sheet, panel or length. Such tendency of the freshly formed leader at the front end of the remainder of the running web can result in advancement of the leader in a wrong direction, i.e., the leader is likely to miss the receiving or intake or inlet end of the mechanism which is to engage and transport successive freshly separated sheets, panels or lengths of flexible material. In many or most instances, the leader behind a freshly separated sheet of paper or like flexible web or strip stock tends to adhere to the lower knife holder or tends to curl so that it is likely to miss the inlet of the transporting unit downstream of the severing station. This can result in lengthy interruptions of operation of one machine or of an entire battery of machines, e.g., if the cross cutter is used in a production line which is designed to turn out steno pads, exercise pads, stacks of wrapped, boxed and crated paper sheets and the like.
German patent application No. 22 61 729 of Ay Kut (published Jul. 4, 1974) discloses a cross cutter which is equipped with hold down devices in the form of air discharging nozzles or in the form of webs or ribs which are provided on the knife holders and serve to curl and thereby stiffen the leader of a running web behind the freshly separated sheet to thus reduce the tendency of the leader to stray by moving in a wrong direction and to thus bypass the sheet transporting unit. A drawback of this proposal is that the reliability of the hold down devices is overly dependent upon the characteristics (such as flexibility) of the running web. Additional problems arise if the hold down devices are utilized in machines which simultaneously process two or more running webs of paper or a like relatively thin and flexible material. Thus, it is necessary to individually adjust each and every one of two or more cross cutters and their hold down devices with attendant losses in time and long interruptions for each change of setup.